Biological information measurement device

ABSTRACT

A biological information measurement device includes a photoplethysmographic sensor that detects a photoplethysmographic signal, an envelope detection processor that generates an envelope of the photoplethysmographic signal, and an amplitude normalization processor that normalizes amplitude of the photoplethysmographic signal to a desired amplitude value based on amplitude of the envelope. The device further includes an adaptive line spectrum enhancer that is capable of varying a filter coefficient, suppressing an aperiodic component contained in the normalized photoplethysmographic signal, and outputting a periodic component. A biological information obtainment unit is provided to obtain biological information such as a pulse rate based on an output signal from the adaptive line spectrum enhancer.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of PCT/JP2014/076761 filedOct. 7, 2014, which claims priority to Japanese Patent Application No.2013-227731, filed Oct. 31, 2013, the entire contents of each of whichare incorporated herein by reference

FIELD OF THE INVENTION

The present invention relates to a biological information measurementdevice.

BACKGROUND

Biological signals such as electrocardiographic waves andphotoplethysmographic waves have characteristics that artifacts (noise)due to body motion or the like is easy to be superimposed thereon.Patent Document 1 discloses a biological signal measurement device thatextracts and detects a pulsation component of a subject from a measuredsignal superimposed with noise components such as an artifact component.

The biological signal measurement device includes a light irradiatorthat irradiates a biological tissue of the subject with two lightcomponents having different wavelengths, a light receiver that receivesthe light components having the respective wavelengths, which have beenemitted from the light irradiator and have transmitted through or havebeen reflected by the biological tissue, and converts the lightcomponents to electric signals (biological signals) in accordance withlight reception intensities of the respective light components, aHilbert transformation unit that performs Hilbert transformation on theelectric signals so as to generate pieces of envelope data formingenvelopes, and an oxygen saturation calculator that calculates anextinction ratio based on the generated pieces of envelope data andcalculates blood oxygen saturation in the artery in the biologicaltissue based on the extinction ratio.

Further, the biological signal measurement device measures the bloodoxygen saturation by detecting the envelopes of the electric signals(biological signals) by the Hilbert transformation unit and performingnormalization processing on amplitudes thereof. In addition, thebiological signal measurement device relatively attenuates componentsother than a frequency component (pulsation component) in accordancewith pulsation of the artery of the subject so as to calculate a pulserate.

Patent Document 1: Japanese Unexamined Patent Application PublicationNo. 2012-024320.

The biological signal measurement device as disclosed in Patent Document1 can deal with unexpected artifacts. However, the biological signalmeasurement device cannot sufficiently remove artifacts for a biologicalsignal with the artifacts superimposed thereon steadily, resulting in arisk that the pulse rate cannot be calculated accurately. Therefore, atechnique capable of removing artifacts more effectively and obtainingbiological information robustly against the artifacts has been desired.

SUMMARY OF THE INVENTION

The present invention has been made in order to solve theabove-described problem and an object thereof is to provide a biologicalinformation measurement device configured to effectively removeartifacts due to body motion or the like, which have been superimposedon a biological signal, and to obtain biological information robustlyagainst the artifacts.

A biological information measurement device according to an aspect ofthe invention includes a biological signal detecting unit that detects abiological signal, an envelope detecting unit that generates an envelopeof the biological signal, an amplitude normalizing unit that normalizesamplitude of the biological signal to a desired amplitude value based onamplitude of the envelope, an adaptive filter that is capable of varyinga filter coefficient, suppresses an aperiodic component contained in thebiological signal normalized by the amplitude normalizing unit, andallows passage of a periodic component, and a biological informationobtainment unit that obtains biological information based on an outputsignal from the adaptive filter.

With the biological information measurement device according to theaspect of the invention, amplitude values of signals which are input tothe adaptive filter can be made substantially constant because theamplitude normalizing unit that normalizes the amplitude of thebiological signal to the desired amplitude value based on the amplitudeof the envelope is provided at a previous stage of the adaptive filter.Therefore, a sum of input power in the adaptive filter is substantiallyconstant and a step-size parameter as a necessary and sufficientcondition for convergence of the adaptive filter can be set previouslywhen a least mean square (LMS) method is used, for example. Further, anadverse effect on the convergence of the adaptive filter by variation inthe amplitude of the biological signal due to individual difference canbe also absorbed. Therefore, the adaptive filter can be made to adaptappropriately so as to extract a frequency component of the biologicalsignal. Further, even when the artifacts are superimposed continuously,they can be removed by the adaptive filter. As a result, artifacts dueto body motion or the like, which have been superimposed on thebiological signal, can be removed effectively and biological informationcan be obtained robustly against the artifacts.

It is preferable that the biological information measurement deviceaccording to the aspect of the invention further include a filtercoefficient updating unit which controls execution and stop of update ofthe filter coefficient of the adaptive filter based on the amplitude ofthe envelope.

According to the exemplary embodiment, execution and stop of the updateof the filter coefficient of the adaptive filter are controlled based onthe amplitude of the envelope. Therefore, inappropriate learning of theadaptive filter can be prevented by controlling (for example, stopping)the update of the filter coefficient appropriately when an excessivelylarge or small biological signal is input.

In the biological information measurement device according to the aspectof the invention, it is preferable that the envelope detecting unitinclude a full-wave rectifying circuit which full-wave rectifies thebiological signal, and a low-pass filter which allows selective passageof a low-frequency component contained in the biological signalfull-wave rectified by the full-wave rectifying circuit and generatesthe envelope of the full-wave rectified biological signal. With this,the envelope of the biological signal can be extracted appropriately.

It is preferable that the biological information measurement deviceaccording to the aspect of the invention further include a basicfrequency amplifying unit which makes peaks remain from an impulsebiological signal detected by the biological signal detecting unit,monotonously decreases the signal between the peaks more moderately thanthe original biological signal, reduces a harmonic component of a basicfrequency contained in the biological signal, amplifies a signalcomponent of the basic frequency, and outputs the signal to the envelopedetecting unit and the amplitude normalizing unit.

In this case, the basic frequency component of the biological signal isamplified. Therefore, even when a biological signal (for example, abiological signal with harmonic waves, such as an impulse sequence (forexample, electrocardiographic waveform and ballistocardiographicwaveform)) having characteristics that the adaptive filter is difficultto adapt for it is input, the adaptive filter can be made to adapt forthe biological signal. Therefore, the biological information can bestably obtained from the biological signal superimposed with artifacts.

It is preferable that the biological information measurement deviceaccording to the aspect of the invention further include a low-passfilter which is interposed at a subsequent stage of the basic frequencyamplifying unit, allows selective passage of the signal component of thebasic frequency contained in the biological signal output from the basicfrequency amplifying unit, and suppresses passage of the harmoniccomponent of the basic frequency.

In this case, a spectrum of the basic frequency of the biological signalcan be further enhanced by applying the low-pass filter to thebiological signal.

According to the invention, artifacts due to body motion or the like,which have been superimposed on a biological signal, can be removedeffectively and biological information can be obtained robustly againstthe artifacts.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating the configuration of a biologicalinformation measurement device according to a first embodiment.

FIG. 2 is a block diagram illustrating the configuration of an adaptiveline spectrum enhancer configuring the biological informationmeasurement device in the first embodiment.

FIG. 3 is a graph illustrating examples of a photoplethysmographicsignal and an envelope signal of the photoplethysmographic signal.

FIG. 4 is a graph illustrating an example of a normalizedphotoplethysmographic signal.

FIG. 5 is a block diagram illustrating the configuration of a biologicalinformation measurement device according to a second embodiment.

FIG. 6 is a circuit diagram of a diode detecting circuit configuring thebiological information measurement device in the second embodiment.

FIG. 7 is a graph illustrating examples of an impulse sequence that isinput to the diode detecting circuit and an output signal waveform ofthe diode detecting circuit.

FIG. 8 is a graph illustrating examples of spectra of the impulsesequence that is input to the diode detecting circuit and an outputsignal from the diode detecting circuit.

FIG. 9 is a graph for explaining another example of a pulsationcomponent amplifying method.

FIG. 10 is a graph illustrating an example of an output signal from anLPF.

DETAILED DESCRIPTION

Hereinafter, preferred embodiments of the invention will be described indetail with reference to the drawings. It should be noted that the samereference numerals denote the same or equivalent portions in thedrawings. In the individual drawings, the same reference numerals denotethe same constituent components and overlapped description thereof isomitted.

First Embodiment

First, the configuration of a biological information measurement device1 according to a first embodiment will be described with reference toFIG. 1 and FIG. 2 in combination. FIG. 1 is a block diagram illustratingthe configuration of the biological information measurement device 1.FIG. 2 is a block diagram illustrating the configuration of an adaptiveline spectrum enhancer 35 configuring the biological informationmeasurement device 1. In the embodiment, the case in which biologicalinformation such as a pulse rate is measured from aphotoplethysmographic signal as a biological signal. It is sufficientthat the biological signal is a signal in which a spectrum of apulsation component is dominant, such as the photoplethysmographicsignal, and the biological signal is not limited to thephotoplethysmographic signal.

The biological information measurement device 1 detects thephotoplethysmographic signal, for example, removes an artifact signalgenerated due to body motion or the like, which has been superimposed onthe photoplethysmographic signal, and measures biological informationsuch as the pulse rate more robustly against artifacts. Therefore, thebiological information measurement device 1 includes aphotoplethysmographic sensor 10 that generates the photoplethysmographicsignal and a signal processing unit 5 that removes the artifact signalsuperimposed on the photoplethysmographic signal and measures thebiological information such as the pulse rate. Hereinafter, individualconstituent components will be described in detail.

The photoplethysmographic sensor 10 is a sensor that optically detectsthe photoplethysmographic signal using light absorption characteristicsof hemoglobin in blood. That is to say, the photoplethysmographic sensor10 functions as a biological signal detecting unit in the scope of thedisclosure herein. The photoplethysmographic sensor 10 is configured byincluding a light-emitting element 11, a light-receiving element 12, anamplifying unit 13, and a driving unit 14.

The light-emitting element 11 emits light in accordance with a pulseddriving signal that is generated and output by the driving unit 14. Forexample, a light emitting diode (LED), a vertical cavity surfaceemitting laser (VCSEL), a resonator-type LED, or the like can be usedfor the light-emitting element 11.

The light-receiving element 12 outputs a detection signal in accordancewith intensity of light that has been emitted from the light-emittingelement 11, has transmitted through a human body such as a finger tip orhas been reflected by the human body, and has been incident thereon. Forexample, a photo diode, a photo transistor, or the like is preferablyused for the light-receiving element 12. In the embodiment, the photodiode is used for the light-receiving element 12. The light-receivingelement 12 is connected to the amplifying unit 13 and the detectionsignal (photoplethysmographic signal) obtained by the light-receivingelement 12 is output to the amplifying unit 13.

The amplifying unit 13 is configured by an amplifier using anoperational amplifier or the like, for example, and amplifies thephotoplethysmographic signal detected by the light-receiving element 12.The photoplethysmographic sensor 10 is connected to the signalprocessing unit 5 and outputs the detected photoplethysmographic signalto the signal processing unit 5.

The signal processing unit 5 applies the adaptive line spectrum enhancer35 as one type of an adaptive filter to the photoplethysmographic signaldetected by the photoplethysmographic sensor 10 to remove an artifactsignal generated due to body motion or the like, which has beensuperimposed on the photoplethysmographic signal, and measures thebiological information such as the pulse rate (basic frequency of thebiological signal). Therefore, the signal processing unit 5 includes apulsation component enhancer 30 that removes an artifact componentcontained in the input photoplethysmographic signal and a biologicalinformation obtainment unit 50 that measures the biological informationsuch as the pulse rate from the photoplethysmographic signal from whichthe artifacts have been removed. Further, the pulsation componentenhancer 30 is configured by including a high-pass filter (HPF) 31, anenvelope detection processor 32, an amplitude normalization processor33, a filter coefficient update controller 34, and the adaptive linespectrum enhancer 35.

Among the above-described individual parts, the amplitude normalizationprocessor 33, the filter coefficient update controller 34, the adaptiveline spectrum enhancer 35, and the biological information obtainmentunit 50 can be functional units or modules that are configured by acentral processing unit (CPU) (or micro controller unit (MCU)) thatperforms arithmetic operation processing, a read only memory (ROM) thatstores therein programs and pieces of data for causing the CPU toexecute pieces of processing, a random access memory (RAM) thattemporarily stores therein pieces of data of various types such asarithmetic operation results, and the like. That is to say, the CPUexecutes the programs stored in the ROM, so that the above-describedindividual functions are made to operate. The present disclosure refersto each specific unit performing its associated algorithm, but it shouldbe appreciated that such algorithms can be performed by the CPUaccording to the exemplary embodiment.

The HPF 31 cuts a direct-current (DC) component of the inputphotoplethysmographic signal. It should be noted that thephotoplethysmographic signal from which the DC component has been cut bythe HPF 31 is output to each of the envelope detection processor 32 andthe amplitude normalization processor 33.

According to an exemplary embodiment, the envelope detection processor32 is comprised by circuitry that includes a full-wave rectifyingcircuit 321 that rectifies the photoplethysmographic signal and alow-pass filter (LPF) 322 that selectively passes a low-frequencycomponent contained in the full-wave rectified photoplethysmographicsignal and generates an envelope of the photoplethysmographic signal.That is to say, the envelope detection processor 32 functions as anenvelope detecting unit in the scope of the disclosure herein. Thus,when the photoplethysmographic signal has a waveform close to a sinewave, an average amplitude value thereof is 2/π-fold of a maximumamplitude value. Therefore, the envelope of the photoplethysmographicsignal is obtained by multiplying the signal which has been full-waverectified and has been subject to the LPF 322 by π/2.

An execution result of an envelope detecting method of this manner isillustrated in FIG. 3. FIG. 3 is a graph illustrating examples of thephotoplethysmographic signal and the envelope signal of thephotoplethysmographic signal. A transverse axis of FIG. 3 indicates time(second) and a longitudinal axis of FIG. 3 indicates amplitude (V). InFIG. 3, the photoplethysmographic signal is indicated by a solid lineand the envelope signal is indicated by a dashed line. It should benoted that the envelope of the photoplethysmographic signal, which hasbeen extracted by the envelope detection processor 32, is output to eachof the amplitude normalization processor 33 and the filter coefficientupdate controller 34.

The amplitude normalization processor 33 normalizes amplitude of thephotoplethysmographic signal to a desired amplitude value based onamplitude (envelope information) of the envelope. That is to say, theamplitude normalization processor 33 functions as an amplitudenormalizing unit in the scope of the disclosure herein. To be morespecific, the amplitude normalization processor 33 normalizes thephotoplethysmographic waves to the desired amplitude value in accordancewith the following equation (1) using the envelope of thephotoplethysmographic waves, which has been obtained by the envelopedetection processor 32:

Equation 1:

ppg _(norm)(t)=d×ppg(t)/env_(ppg)(t)   (1)

wherein d indicates the desired amplitude value, ppg(t) indicates thephotoplethysmographic signal to which the HPF 31 has been applied,env_(ppg)(t) indicates the envelope signal of ppg(t), and ppg_(norm)(t)indicates the normalized photoplethysmographic signal.

A waveform normalized in accordance with the equation (1) is illustratedin FIG. 4 (in the case of d=1.0). FIG. 4 is a graph illustrating anexample of the normalized photoplethysmographic signal. A transverseaxis of FIG. 4 indicates time (second) and a longitudinal axis of FIG. 4indicates amplitude (V). It should be noted that thephotoplethysmographic signal normalized by the amplitude normalizationprocessor 33 is output to the adaptive line spectrum enhancer 35.

The filter coefficient update controller 34 controls execution and stopof the process of updating a filter coefficient of the adaptive linespectrum enhancer 35 based on the amplitude (envelope information) ofthe envelope of the photoplethysmographic signal. To be more specific,when the amplitude value of the envelope of the photoplethysmographicsignal is larger than a first threshold value or the amplitude value ofthe envelope of the photoplethysmographic signal is smaller than asecond threshold value (first threshold value>second threshold value),the filter coefficient update controller 34 stops the update of thefilter coefficient of the adaptive line spectrum enhancer 35. On theother hand, when the amplitude value of the envelope of thephotoplethysmographic signal is equal to or smaller than the firstthreshold value and equal to or larger than the second threshold value,the filter coefficient update controller 34 updates the filtercoefficient of the adaptive line spectrum enhancer 35. That is to say,the filter coefficient update controller 34 functions as a filtercoefficient updating unit in the scope of the disclosure herein. Itshould be noted that a control signal of the filter coefficient from thefilter coefficient update controller 34 is output to the adaptive linespectrum enhancer 35.

The adaptive line spectrum enhancer 35 is one type of the adaptivefilter and adapts so as to enhance a linear spectrum on a frequencyaxis. In other words, the adaptive line spectrum enhancer 35 isconfigured to vary the filter coefficient, suppress an aperiodiccomponent (for example, artifacts) contained in the normalizedphotoplethysmographic signal, and allow passage of a periodic component(for example, pulsation component). Further, a cycle of a pulsationinterval obtained from the biological signal fluctuates finely even atthe rest and a signal of the harmonic component contained in thepulsation signal is therefore suppressed to some extent. The adaptiveline spectrum enhancer 35 functions as an adaptive filter in the scopeof the disclosure herein. To be more specific, according to theexemplary embodiment, the adaptive line spectrum enhancer 35 includes adelay unit 351, an adaptive filter 352, and an adder 353, as illustratedin FIG. 2.

In the adaptive line spectrum enhancer 35 as illustrated in FIG. 2, theadaptive filter 352 minimizes a mean square error (MSE) of an errorsignal e[n] as difference between a desired signal d[n] and an outputsignal y[n], suppresses the aperiodic component (for example, bodymotion artifacts) contained in the input signal (photoplethysmographicsignal), and allows passage of the periodic component (for example, aperiodic signal such as photoplethysmographic waves). Further, the delayunit 351 in FIG. 2 is a correlation isolation parameter for removing acorrelation present between a noise component of an input signal x[n]and a delayed input signal. The adaptive line spectrum enhancer 35 isconnected to the biological information obtainment unit 50 and theoutput signal from the adaptive line spectrum enhancer 35 is output tothe biological information obtainment unit 50. In the embodiment, theadaptive filter 352 employing a fixed point arithmetic operation is usedin order to reduce load of an arithmetic operation.

The biological information obtainment unit 50 obtains the biologicalinformation such as the pulse rate and the pulse interval, for example,based on the output signal from the adaptive line spectrum enhancer 35from which the artifacts have been removed. That is to say, thebiological information obtainment unit 50 functions as a biologicalinformation obtainment unit in the scope of the disclosure herein. Itshould be noted that the obtained biological information such as thepulse rate is output to the outside or is stored in the above-describedRAM.

With the above-described configuration, in the biological informationmeasurement device 1, first, the HPF 31 cuts the DC component of theinput photoplethysmographic signal. Then, the envelope detectionprocessor 32 detects the envelope of the photoplethysmographic signaland calculates the amplitude value of the envelope of thephotoplethysmographic signal. As described above, in the embodiment, theenvelope of the photoplethysmographic signal is calculated by full-waverectifying the photoplethysmographic signal and applying the LPF 322 tothe obtained signal.

Subsequently, the amplitude normalization processor 33 normalizes thephotoplethysmographic waves to the desired amplitude value in accordancewith the above equation (1) based on the amplitude value of thecalculated envelope of the photoplethysmographic signal. Thereafter, theadaptive line spectrum enhancer 35 suppresses the aperiodic component(for example, artifacts) contained in the normalizedphotoplethysmographic signal and outputs only the periodic component(for example, pulsation component). It should be noted that as describedabove, the filter coefficient update controller 34 controls updating ofthe filter coefficient of the adaptive line spectrum enhancer 35.

Then, the biological information obtainment unit 50 obtains thebiological information such as the pulse rate and the pulse interval,for example, based on the output signal from the adaptive line spectrumenhancer 35. Thus, the normalization processing by the envelopedetection and the adaptive line spectrum enhancer 35 (adaptive filter352) are combined so as to remove the artifact signal superimposed onthe photoplethysmographic signal and extract the pulsation componentonly.

The embodiment provides an advantage that the LMS method with reducedarithmetic operation load can be employed for the adaptive filter 352 bynormalizing the amplitude of the photoplethysmographic waves. The LMSmethod needs setting of the step-size parameter μ in a range satisfyinga convergence condition defined by the following equation (2):

$\begin{matrix}{{Equation}\mspace{14mu} 2} & \; \\{0 < \mu < \frac{2}{\sum\limits_{k = 0}^{M}{E\left\{ {x^{2}\left\lbrack {n - k} \right\rbrack} \right\}}}} & (2)\end{matrix}$

wherein μ indicates the step-size parameter of the adaptive filter 352,M indicates an order of the adaptive filter 352, x indicates an inputbiological signal to the adaptive filter 352, and E{ } indicates anarithmetic operation of an expected value.

However, a term (sum of input power) expressed by E in the equation (2)for an aperiodic signal containing the body motion artifacts ispreviously unknown. In the embodiment, the input photoplethysmographicsignal is normalized and has substantially constant amplitude.Therefore, when the order M in the equation (2) is large, the sum of theinput power is substantially constant and the step-size parameter μ asthe necessary and sufficient condition for convergence of the adaptivefilter 352 can be set previously. Further, an adverse effect on theconvergence of the adaptive filter 352 by variation in the amplitude ofthe photoplethysmographic signal (biological signal) due to differenceamong individuals using the biological information measurement device 1can be also absorbed.

Therefore, the adaptive filter 352 can be made to adapt appropriately soas to extract only the frequency of the biological signal. Further, evenwhen the artifacts are superimposed continuously, they can be removed bythe adaptive filter 352. As a result, the artifacts due to body motionor the like, which have been superimposed on the biological signal, canbe removed effectively and the biological information can be obtainedrobustly against the artifacts.

In addition, the embodiment provides an advantage that a dynamic rangeof a signal which is input to the adaptive line spectrum enhancer 35(adaptive filter 352) at the subsequent stage can be determined bynormalizing the amplitude of the photoplethysmographic signal. Ingeneral, it is difficult for a low-end MCU to execute a floating pointarithmetic operation of the adaptive filter 352 because of thearithmetic operation load. For this reason, the fixed point arithmeticoperation is required, and in this case, trade-off between arithmeticoperation accuracy of the fixed point arithmetic operation for thedynamic range of the input signal and overflow becomes a problem. When abit number of a decimal part is made large in order to ensure thearithmetic operation accuracy of the fixed point arithmetic operation,overflow occurs in the fixed point arithmetic operation if a largeamplitude value is input for the input signal and an accurate arithmeticoperation result cannot be obtained. By contrast, when the bit number ofthe decimal part is made small, arithmetic operation errors areaccumulated, resulting in a possibility that the adaptive filter 352diverges. In the embodiment, normalization of the biological signal tothe desired amplitude value at the previous stage of the adaptive filter352 enables an optimum bit number and an optimum type of the variable ofthe fixed point arithmetic operation to be determined when the fixedpoint arithmetic operation is designed. Accordingly, the problem of thedynamic range, which occurs in the fixed point arithmetic operation, canbe solved, thereby using the adaptive filter by the low-end MCU.

Moreover, the embodiment provides an advantage that the update of thefilter coefficient of the adaptive line spectrum enhancer 35 (adaptivefilter 352) can be controlled by using the amplitude value detected bythe envelope detection. The normalization processing of the amplitudecauses the spectrum of the artifact component to decrease after thenormalization. However, when an excessively large or smallphotoplethysmographic signal is input continuously, a section with anextremely bad SN ratio of the signal lasts, resulting in a possibilitythat learning of the adaptive filter 352 is adversely influenced. Inorder to solve this disadvantage, the filter coefficient updatecontroller 34 detects the excessively large or small amplitude value ofthe photoplethysmographic signal using the output value of the envelopedetection processor 32 and operates so as not to update the filtercoefficient, thereby preventing inappropriate learning of the adaptivefilter 352. In particular, the method using the envelope information fordetermining the excessively large or small signal utilizes aninstantaneous amplitude value of the signal unlike a method using anabsolute value of the signal simply for the determination. Therefore,the method can make the determination using a constant amplitude valuecontinuously even at a zero-cross point of the signal and a signalaverage value.

Second Embodiment

Next, the configuration of a biological information measurement device 2according to a second embodiment will be described with reference toFIG. 5 and FIG. 6 in combination. Description of the configurations sameas or similar to those of the biological information measurement device1 in the above-described first embodiment are omitted and differentpoints are described mainly. FIG. 5 is a block diagram illustrating theconfiguration of the biological information measurement device 2 in thesecond embodiment. In FIG. 5, the same reference numerals denoteconstituent components that are the same as or equivalent to those inthe first embodiment. FIG. 6 is a circuit diagram of a pulsationcomponent amplifying unit 20 (diode detecting circuit 21) configuringthe biological information measurement device 2.

The biological information measurement device 2 is different from theabove-described biological information measurement device 1 in thefollowing point. That is, in the biological information measurementdevice 2, the pulsation component amplifying unit 20 and a low-passfilter (LPF) 22 are provided at previous stages of the pulsationcomponent enhancer 30 (HPF 31). They are provided in order to easilyadapt to a biological signal with harmonic waves having, as a basicfrequency, a pulsation component of an electrocardiographic waveform ora ballistocardiographic waveform for which the adaptive line spectrumenhancer 35 (adaptive filter 352) is difficult to adapt. Further, thebiological information measurement device 2 is different from theabove-described biological information measurement device 1 also in thefollowing point. That is, the biological information measurement device2 includes a pair of electrocardiographic electrodes 15 and 16 (firstelectrocardiographic electrode 15 and second electrocardiographicelectrode 16) for detecting an electrocardiographic signal as thebiological signal, instead of the photoplethysmographic sensor 10. Otherconfigurations of the biological information measurement device 2 arethe same as or similar to those of the above-described biologicalinformation measurement device 1, and detail description thereof isomitted.

The first electrocardiographic electrode 15 and the secondelectrocardiographic electrode 16 detect the electrocardiographicsignal, and obtain the electrocardiographic signal in accordance withpotential difference between right and left hands of a user when theright and left hands (finger tips) of the user make contact with them.That is to say, the first electrocardiographic electrode 15 and thesecond electrocardiographic electrode 16 also correspond to thebiological signal detecting unit in the scope of the disclosure herein.Each of the first electrocardiographic electrode 15 and the secondelectrocardiographic electrode 16 is connected to the pulsationcomponent amplifying unit 20 and the detected electrocardiographicsignal is amplified by an amplifier (not illustrated), and then, isinput to the pulsation component amplifying unit 20.

In the embodiment, the diode detecting circuit 21 as illustrated in FIG.6 is used for the pulsation component amplifying unit 20. The diodedetecting circuit 21 makes peaks remain from an impulse biologicalsignal (electrocardiographic signal) detected by the firstelectrocardiographic electrode 15 and the second electrocardiographicelectrode 16, monotonously decreases the signal between the peaks moremoderately than the original biological signal, reduces a harmoniccomponent of a basic frequency contained in the electrocardiographicsignal, enhances a signal component of the basic frequency, and outputsthe obtained signal to the pulsation component enhancer 30 (to be morespecific, outputs the obtained signal to the envelope detectionprocessor 32 and the amplitude normalization processor 33 through theLPF 22 and the HPF 31). The diode detecting circuit 21 (pulsationcomponent amplifying unit 20) functions as a basic frequency amplifyingunit as disclosed herein.

Examples of an impulse sequence that is input to the diode detectingcircuit 21 (pulsation component amplifying unit 20) and an output signalwaveform of the diode detecting circuit 21 are illustrated in FIG. 7. Inorder to simplify the description, the biological signal that is inputis assumed to an impulse sequence (60 [bpm], sampling frequency 100[Hz]) synchronous with pulsation. A transverse axis of FIG. 7 indicatestime (second) and a longitudinal axis of FIG. 7 indicates amplitude (V).In FIG. 7, the output signal waveform is indicated by a solid line andthe impulse sequence (input signal) is indicated by a dashed line. Asillustrated in FIG. 7, the diode detecting circuit 21 is applied to theimpulse sequence, so that a waveform with amplified frequency of thepulsation component of the impulse sequence is obtained.

FIG. 8 illustrates examples of spectra of the impulse sequences beforeand after the pulsation component amplification processing, which havebeen calculated by fast Fourier transform (FFT), that is, the spectrumof the impulse sequence that is input to the diode detecting circuit 21(pulsation component amplifying unit 20) and the spectrum of an outputsignal from the diode detecting circuit 21. A transverse axis of FIG. 8indicates frequency (Hz) and a longitudinal axis of FIG. 8 indicatesamplitude. In FIG. 8, the spectrum of the output signal is indicated bya solid line and the spectrum of the impulse sequence (input signal) isindicated by a dashed line. With reference to FIG. 8, it is found thatthe spectrum of the pulsation component at 1 [Hz] is amplified after thediode detection processing (note that a DC component is cut from thesignal after the pulsation component amplification processing, and then,the spectrum thereof is calculated).

The diode detecting circuit 21 is not used for detecting the envelopenormally but for amplifying the spectrum of the pulsation component bydischarging electric charges accumulated in a capacitor C to some extentwithout holding the impulse sequence between the peaks intentionally.Therefore, a constant of the diode detecting circuit 21 as illustratedin FIG. 6 needs to be set to such constant that the electric chargesaccumulated in the capacitor C are discharged to some extent even whenthe electrocardiographic signal corresponding to a measureable maximumpulse rate in specification is input. It should be noted that signalprocessing in the diode detecting circuit 21 may be executed not by anelectric circuit but by digital signal processing.

Further, the pulsation component amplifying unit 20 may not beconfigured by the diode detecting circuit 21 and may perform thefollowing processing. That is, the pulsation component amplifying unit20 may perform processing of functioning like the diode detectingcircuit 21 in the case in which a voltage of the input signal isincreased and generating sawtooth waves so as to monotonously decreasethe signal by a constant inclination in the case in which the voltage ofthe input signal is decreased. FIG. 9 is a graph for explaining anotherexample of the pulsation component amplifying method. A transverse axisof FIG. 9 indicates time (second) and a longitudinal axis of FIG. 9indicates amplitude (V). In FIG. 9, an output signal waveform isindicated by a solid line and an impulse sequence (input signal) isindicated by a dashed line.

Application of the diode detecting circuit 21 (pulsation componentamplifying unit 20) provides an effect that the spectrum of thepulsation component is amplified and an effect that an artifact signalsmaller than the signal after the pulsation component amplification asillustrated in FIGS. 7 and 9 can be removed as a result. With this, asignal robust against the artifacts can be obtained. Further, anartifact signal larger than the signal after the pulsation componentamplification as illustrated in FIGS. 7 and 9 is also reduced by theadaptive line spectrum enhancer 35 (adaptive filter 352) at thesubsequent stage. It should be noted that the output signal from thediode detecting circuit 21 is output to the LPF 22.

The LPF 22 is provided at a subsequent stage of the diode detectingcircuit 21, allows selective passage of the signal component of thebasic frequency contained in the electrocardiographic signal output fromthe diode detecting circuit 21, and suppresses passage of the harmoniccomponent (high-frequency component) of the basic frequency. When ameasureable maximum pulse rate in specification is set to 200 [bpm], acutoff frequency of the LPF 22 is preferably set to be equal to orhigher than 3.333 [Hz]. A signal waveform when the LPF 22 is applied tothe signal after experienced the diode detecting circuit 21 isillustrated in FIG. 10. FIG. 10 is a graph illustrating an example ofthe output signal from the LPF 22. A transverse axis of FIG. 10indicates time (second) and a longitudinal axis of FIG. 10 indicatesamplitude (V). The output signal from the LPF 22 is output to thepulsation component enhancer 30. The configurations of the pulsationcomponent enhancer 30 and the biological information obtainment unit 50are the same as or similar to those of the above-described biologicalinformation measurement device 1, and detail description thereof istherefore omitted.

Thus, even the biological signal with the harmonic waves having, as thebasic frequency, the pulsation component of the electrocardiographicwaveform or the ballistocardiographic waveform for which the adaptiveline spectrum enhancer 35 (adaptive filter 352) is difficult to adaptnormally can be converted into a signal (signal having the pulsationcomponent as a main component) for which the adaptive line spectrumenhancer 35 (adaptive filter 352) is easy to adapt by applying thepulsation component amplifying unit 20 (diode detecting circuit 21) andthe LPF 22 to the signal.

As described above, with the embodiment, the basic frequency componentof the electrocardiographic signal is amplified by the pulsationcomponent amplifying unit 20 (diode detecting circuit 21). Therefore,even when the biological signal (for example, the biological signal withthe harmonic waves of the electrocardiographic waveform or theballistocardiographic waveform) having characteristics that the adaptivefilter 352 is difficult to adapt for it is input, the adaptive filter352 can be made to adapt for the biological signal. Accordingly, thebiological information can be obtained stably from the biological signalsuperimposed with the artifacts.

In addition, in the embodiment, the spectrum of the basic frequency ofthe electrocardiographic signal can be further enhanced by applying theLPF 22 to the electrocardiographic signal output from the diodedetecting circuit 21. Note that the LPF 22 allows selective passage ofthe signal component of the basic frequency contained in theelectrocardiographic signal and suppresses passage of the harmoniccomponent of the basic frequency.

Although the embodiments of the invention have been described above, theinvention is not limited to the above-described embodiments and variousmodifications can be made. For example, in the above-describedembodiments, the method using the full-wave rectifying circuit 321 andthe LPF 322 is employed as the envelope detection method. Alternatively,instead of the method, for example, various methods such as a methodusing a diode detecting circuit, a method using a synchronous detectingcircuit, a method in which an input signal is squared, and then, the LPFis applied to the signal, and a method in which instantaneous amplitudeis calculated from an analysis signal by a Hilbert transformation deviceor quadrature demodulation can be used.

Although in the above-mentioned embodiments, a method in which theupdate of the filter coefficient is stopped based on the thresholdvalues is employed in the update control of the filter coefficient ofthe adaptive filter 352 based on the envelope information (the amplitudevalue of the envelope), for example, a method in which the step-sizeparameter in accordance with the amplitude value is dynamically set maybe used instead of the method. In this case, the reference to thestep-size parameter in accordance with the amplitude value can beperformed by a method involving calculating the step-size parameter fromthe amplitude value or a method involving referring to a lookup tablethat is previously stored.

REFERENCE SIGNS LIST

1, 2 BIOLOGICAL INFORMATION MEASUREMENT DEVICE

5, 6 SIGNAL PROCESSING UNIT

10 PHOTOPLETHYSMOGRAPHIC SENSOR

15 FIRST ELECTROCARDIOGRAPHIC ELECTRODE

16 SECOND ELECTROCARDIOGRAPHIC ELECTRODE

20 PULSATION COMPONENT AMPLIFYING UNIT

21 DIODE DETECTING CIRCUIT

22 LPF

30 PULSATION COMPONENT ENHANCER

31 HPF

32 ENVELOPE DETECTION PROCESSOR

321 FULL-WAVE RECTIFYING CIRCUIT

322 LPF

33 AMPLITUDE NORMALIZATION PROCESSOR

34 FILTER COEFFICIENT UPDATE CONTROLLER

35 ADAPTIVE LINE SPECTRUM ENHANCER

351 DELAY UNIT

352 ADAPTIVE FILTER

50 BIOLOGICAL INFORMATION ACQUIRING UNIT

1. A biological information measurement device comprising: a biologicalsignal detecting unit configured to detect a biological signal; anenvelope detecting circuit that receives the biological signal andgenerates an envelope of the biological signal; and a computerprocessing unit configured to: normalize an amplitude of the biologicalsignal based on an amplitude of the envelope, filter an aperiodiccomponent contained in the normalized biological signal and output aperiodic component of the normalized biological signal, and obtainbiological information based on the periodic component of the normalizedbiological signal.
 2. The biological information measurement deviceaccording to claim 1, wherein the computer processing unit comprises anadaptive filter having a variable filter coefficient for filtering theaperiodic component contained in the normalized biological signal. 3.The biological information measurement device according to claim 2,wherein the computer processing unit further comprises: a delay devicecoupled to an input of the adaptive filter and configured to delay thenormalized biological signal; and an adder coupled to an output of theadaptive filter, wherein the adaptive filter minimizes a mean squareerror of an error signal output by the adder as difference between adesired signal and an output signal of the adaptive filter.
 4. Thebiological information measurement device according to claim 2, whereinthe computer processing unit is further configured to update thevariable filter coefficient of the adaptive filter based on theamplitude of the envelope.
 5. The biological information measurementdevice according to claim 4, wherein the computer processing unit stopsthe update of the variable filter coefficient when the amplitude of theenvelope is larger than a first threshold value or smaller than a secondthreshold value.
 6. The biological information measurement deviceaccording to claim 1, wherein the envelope detecting circuit includes: afull-wave rectifying circuit that rectifies the biological signal, and alow-pass filter passes a low-frequency component contained in therectified biological signal and generates the envelope of the rectifiedbiological signal.
 7. The biological information measurement deviceaccording to claim 1, further including a frequency amplifying unit thatmaintains peaks from an impulse biological signal detected by thebiological signal detecting unit, monotonously decreases the signalbetween the peaks, reduces a harmonic component of a basic frequencycontained in the biological signal, amplifies a signal component of thebasic frequency, and outputs the signal to the envelope detectingcircuit and the computer processing unit.
 8. The biological informationmeasurement device according to claim 7, further including a low-passfilter interposed at a subsequent stage of the frequency amplifyingunit, wherein the low-pass filter passes the signal component of thebasic frequency contained in the biological signal output from thefrequency amplifying unit, and filters the harmonic component of thebasic frequency.
 9. The biological information measurement deviceaccording to claim 8, wherein the biological signal detecting unitcomprises a pair of electrocardiographic electrodes configured to detectthe biological signal and coupled to an input of the frequencyamplifying unit.
 10. The biological information measurement deviceaccording to claim 9, wherein the frequency amplifying unit comprises adiode detecting circuit have at least one diode coupled to one of thepair of electrocardiographic electrodes and a resistor and capacitoreach coupled in parallel to respective outputs of the pair ofelectrocardiographic electrodes.
 11. The biological informationmeasurement device according to claim 1, wherein the biological signaldetecting unit comprises a sensor having a light emitting unit thatemits light based on a pulsed driving signal, a light receiving unitthat outputs a detection signal based on an intensity of light emittedfrom the light-emitting element, and an amplifying unit that amplifiesthe detection signal.
 12. The biological information measurement deviceaccording to claim 11, further comprising a high-pass filter thatfilters a direct-current component of the amplified signal and outputsthe filtered signal as the biological signal to the envelope detectingcircuit and the computer processing unit.
 13. A method for measuringbiological information, the method comprising: detecting, by abiological signal detecting unit, a biological signal; generating, by anenvelope detecting circuit, an envelope of the biological signal;normalizing, by a computer processing unit, an amplitude of thebiological signal based on an amplitude of the envelope; filtering, byan adaptive filter having a variable filter coefficient, an aperiodiccomponent contained in the normalized biological signal and outputting aperiodic component of the normalized biological signal; and obtaining,by the computer processing unit, biological information based on theperiodic component of the normalized biological signal.
 14. The methodfor detecting biological information according to claim 13, furthercomprising, updating, by the computer processing unit, the variablefilter coefficient of the adaptive filter based on the amplitude of theenvelope.
 15. The method for detecting biological information accordingto claim 14, further comprising, stopping, by the computer processingunit, the update of the variable filter coefficient when the amplitudeof the envelope is larger than a first threshold value or smaller than asecond threshold value.
 16. The method for detecting biologicalinformation according to claim 13, further comprising: a full-waverectifying, by the envelope detecting circuit, the biological signal;and passing, by the envelope detecting circuit, a low-frequencycomponent contained in the rectified biological signal to generate theenvelope of the rectified biological signal.
 17. The method fordetecting biological information according to claim 13, furthercomprising: maintaining, by a frequency amplifying unit, peaks from animpulse biological signal detected by the biological signal detectingunit; monotonously decreasing, by the frequency amplifying unit, thesignal between the peaks; reducing, by the frequency amplifying unit, aharmonic component of a basic frequency contained in the biologicalsignal; amplifying, by the frequency amplifying unit, a signal componentof the basic frequency; and outputting, by the frequency amplifyingunit, the signal to the envelope detecting circuit and the computerprocessing unit.
 18. The method for detecting biological informationaccording to claim 17, further comprising: passing, by a low-pass filterinterposed at a subsequent stage of the frequency amplifying unit, thesignal component of the basic frequency contained in the biologicalsignal output from the frequency amplifying unit; and filtering, by thelow-pass filter, the harmonic component of the basic frequency.
 19. Themethod for detecting biological information according to claim 18,wherein the biological signal detecting unit comprises a pair ofelectrocardiographic electrodes for detecting the biological signal. 20.The method for detecting biological information according to claim 13,further comprising: filtering, by a high-pass filter, a direct-currentcomponent of the biological signal detecting by the biological signaldetecting unit; and outputting the filtered signal as the biologicalsignal to the envelope detecting circuit and the computer processingunit.